1. Field of the Invention
The present invention relates to a combustion-engined setting tool for driving fastening elements in a constructional component and including a combustion chamber for an oxidant-fuel gas mixture and having at least one axially displaceable wall, a guide cylinder adjoining the combustion chamber, a setting piston displaceable in the guide cylinder, a press-on element, and a transmission device for connecting the press-on element with the at least one combustion chamber wall for axially displacing same in response to a press-on stroke of the press-on element.
2. Description of the Prior Art
Setting tools of the type described above are operated with gaseous or liquid fuels that should be evaporated before combustion. The setting energy for driving in a fastening element by a setting piston. The oxidant is, e.g., oxygen of the environmental air. Before each setting process, therefore, fresh air should be brought into the combustion chamber and after each setting process, the flue gas, which is produced by combustion, should be removed from the combustion chamber.
In order to be able to carry out a setting process, the setting tool should be pressed against a constructional component to prevent actuation of the setting tool without a contact with the constructional component. The press-on stroke should be as small as possible for ergonomical reasons.
German Publication DE 40 32 203 A1 discloses a combustion-engined setting tool including a combustion chamber for combusting an air-fuel mixture and a setting piston displaceable in a guide cylinder and driven by a working pressure produced by the combustion of the air-fuel mixture. The combustion chamber is located in a first section of the setting tool housing, with the second housing section being displaceable relative to the first housing section. Further, the guide cylinder is likewise displaceable relative to the combustion chamber, being displaceable by an intermediate rack-and-pinion gear upon displacement of the second housing section relative to the first housing section. The relative movement of the second housing section relative to the first housing section upon pressing of the setting tool against the constructional component, provides for displacement of the guide cylinder away from the combustion chamber and, thus, for expansion of the combustion chamber volume.
The combustion chamber is divided in sub-chambers. These sub-chambers are separated by at least one displaceable intermediate or separation wall displaceable together with the guide cylinder. For evacuating the flue gases from the combustion space, the guide cylinder is displaced, together with an arranged thereon, combustion chamber wall, into the combustion chamber, reducing the volume of both sub-chambers to a minimum. The intermediate wall is displaced together with the guide cylinder. The flue gases are removed from the setting tool. When the sub-chambers are displaced away from each other, when the setting tool is again pressed against a constructional component, the sub-chambers are filled with fresh air.
The drawback of the known setting tool is a complicated and expensive to produce, mechanics that provides for expansion of the combustion volume in the combustion chamber.
In a setting tool Hilti GX 100 of the assignee herein, a setting piston is displaced in a piston guide that is adjoined, in the drive-in direction, by a bolt guide. At its end opposite the bolt guide, the piston guide is adjoined by a combustion chamber having a rear wall coaxially displaceable relative to the combustion chamber. When the setting tool is pressed against a constructional component, the rear wall of the combustion chamber is displaced away from the piston cylinder, and the return springs are compressed, whereby the combustion chamber is expanded.
Simultaneously with the expansion of the combustion chamber, it is filled with fresh air. The press-on path is equal to the path of displacement of the combustion chamber rear wall away from the piston cylinder that is equal to the axial length of the combustion chamber. After completion of the setting process and lifting of the setting tool off the constructional component, the combustion chamber rear wall moves back into its initial position under the biasing forces of the return springs, whereby the flue gases are expelled upon collapse of the combustion chamber. The advantage of the above-described setting tool consists in that no accumulator or battery is needed as evacuation of the combustion chamber is effected mechanically.
However, the above-described setting tool has a relatively long press-on path and a relatively large diameter of the combustion chamber.
European Patent EP 0 711 634 B1 discloses a combustion-engined setting tool having a combustion chamber for combusting a fuel gas-air mixture, with ventilator means provided in the combustion chamber for creating turbulence. The ventilator means is driven by an electric motor that is supplied with an electrical energy by a battery.
The use of the ventilator means for rinsing the combustion chamber permits to keep the press-on path rather short.
The drawback of this setting tool consists of its large weight resulting from the need of a battery or accumulator and of the need to replace them when their energy dies out.
Accordingly, an object of the present invention is to provide a setting tool of the type described above in which the drawbacks of the known setting tools are eliminated.